The present invention relates to a seat back for an automotive seat with an integrated protective device to prevent injuries, especially cervical syndrome and whiplash, caused by a rear-end impact.
Modern developments in automotive engineering frequently make use of the materials and structural methods available to build the seat-back parts of automotive seats with low weight but with high stiffness to withstand the high strains occurring in an accident and to adequately support a seat occupant. An injury to the cervical musculature and cervical vertebral column of a seat occupant can occur, however, in a so-called bumper-thumper at low speed in the range of 10 to 30 km/hr. (low speed crash) in which the body undergoes a relatively low acceleration (about 8-20 g), because the impact force acts nearly uncushioned upon the seat occupant. An undesired so-called whipping effect may occur on the head and neck that leads to an overstretching and overstraining of the cervical vertebral column and the cervical musculature. This effect and the possible spinal column injuries, especially around the neck, are known by the English term xe2x80x9cwhiplash.xe2x80x9d
Passive and active devices to protect against whiplash are known, wherein active devices are supposed to actively shorten the distance between the head of the seat occupant and head restraint of the seat back in case of an accident. The reference D19743339AI describes such a known active device. In this reference, the body of the seat occupant, which is accelerated due to its inertia into the seat back of the automotive seat or is bent backwards in a collision, strikes a baffle plate installed underneath the swiveling axis of the top seat-back part and connected with a swivel mount to the top seat-back part, especially with a head restraint. The head restraint swings forward from the relative motion of the baffle plate to the rear. The motion of the head restraint is supposed to mitigate the action of the whipping effect.
A disadvantage in this technique is that the relative motion of the head restraint is activated by the seat occupant being flung into the seat back. The top seat-back part can thereby only be accelerated in the pivot direction by a value that at most equals the acceleration that the seat occupant experiences from the collision. But since the motion of the seat occupant can""t be precisely predicted in every case, incorrect and undesired effects could therefore occur from the active counter movement of the seat back and head restraint, depending on the circumstances. The impact of the seat occupant can thus even be strengthened, and the seat occupant can not be prevented from rising up (vertical motion upwards within the seat). In a rear-end impact, the seat occupant is flung into the seat back, which is inclined towards the back most of the time, in such a manner that the seat occupant tends to rise up on the seat back, like a ramp. In the conventional techniques of the art, this causes the seat back to fail, snapping from overload, and no longer being capable of supporting the seat occupant. In particular, the head of the seat occupant can end up in such a high position, above the head restraint, where it can no longer be supported. A considerable accident residual risk therefore exists in the case of the conventional seat back.
It is the objective of the present invention to create, with inexpensive structural means, a seat back of the type mentioned, whose protective device ensures improved protection of the seat occupant against injury, especially by improving the possibility of interception and cushioning when the head and upper body of the seat occupant strikes the head restraint or seat back.
It is additionally the objective of the present invention to create, with inexpensive means, a process of the type mentioned, with which the accident residual risk can be substantially reduced compared to the known techniques in the art.
In the seat back according to invention, the protective device first features a device that generates a torque operating on the top seat-back part in the pivot direction, regardless whether the automotive seat is occupied, and secondly features means for detecting a rear-end impact that is actively linked with the torque-generating device in such a way that the device is activated in the event of a rear-end impact and the swinging movement is started.
In the process according to invention, the top seat-back part is accelerated in the pivot direction at a considerable rate. The acceleration rate that the automotive seat will primarily experience from a rear-end impact will preferably lie in the range of about 60 to 200 m/sec2, preferably in the range of about 60 to 90 m/sec2. The process according to invention can be carried out to advantage with the seat back according to invention, since the protective device isn""t activated by the seat occupant, but by the means for detecting the rear-end impact in cooperation with the device that generates the torque operating on the top seat-back part.
At the same time, the swinging of the top seat-back part can preferably commence quickly enough that the top seat-back part will be situated in its safety position before the movement of the head of the seat occupant caused by the rear-end impact. In its safety position, the top seat-back part lies directly against the body of the seat occupant, so that, in spite of the acceleration operating upon the seat occupant from the collision, the seat occupant advantageously can no longer move freely backwards, opposite the direction of vehicular travel, and sustain injuries from the accident.
The swinging of the top seat-back part out of its standard use position into its safety position can preferably be completed approximately 35 to 60 ms after the rear-end impact, and after this time the top seat-back part can preferably be situated in its safety position in the state of rest or nearly in the state of rest. This is possible, since the means for detecting the rear-end impact, such as an acceleration sensor, can be designed such that it becomes operative within about 8 to 17 ms. The torque-generating device can thereby be activated 15 to 33 ms after the rear-end impact and the safety position can be achieved after the extremely short time span mentioned above. A state of rest of the top seat-back portion, preferably in the safety position, will assure that the counter movement of the top seat-back part and the body of the seat occupant will be minimized when they meet.
In the seat back according to invention, it is particularly preferable in regard to the efficiency of the protective device, for a head restraint to be fastened in or on the top seat-back part. However, the top seat-back part can also be designed in such a manner that it takes over the function of a head restraint. In any case, the seat occupant can thereby move into the back support uniformly under conditions of decelerating energy absorption by the automotive seat, especially for special protection of the head and neck region.
In addition, a system that acts purely passively can be applied in the seat back at the same time if necessary, such as a system that automatically fits itself optimally to the seat occupant and the contours of the back, the shoulders, and/or the head of the seat occupant while the accident is occurring, whereby the kinetic energy is converted to deformation work (plastic expansion/upsetting).
It is currently endeavored to situate head restraints into a so-called comfort position, in which their distance to the head of the seat occupant is about 80 to 120 mm, when the seat back is in its standard use position. By swinging the top seat-back part, the head restraint is then moved into a so-called intercept position, in which its distance to the head of the seat occupant is zero or nearly zero. When a head restraint is present, everything stated above or below about the standard use position and the safety position of the top seat-back part consequently also applies to the comfort and intercept positions of the head restraint.
Another meaningful advantage of the invention consists of the fact that the seat occupant can be prevented from rising up in the seat during a rear-end impact, because the safety position of the top seat-back part, or the intercept position of the head restraint respectively, occurs at the right time.